Early prophylactic antivirals reduced H1N1 household transmissionEarly antiviral prophylaxis reduced the secondary attack rate (SAR) of pandemic 2009 H1N1 flu from 10.6% to 4.5%, and giving antivirals to household members was 92% effective, according to a study published today. In the observational cohort study, UK researchers followed 285 confirmed 2009 H1N1 cases in 259 households with 761 contacts. UK officials had implemented a policy of administering antiviral drugs to both patients and their close contacts. At 2 weeks, the confirmed SAR was 8.1% (62/761) and significantly higher in children 16 years and younger than in contacts 50 and older (18.9% vs 1.2%, P<0.001). But giving index case-patients antiviral drugs within 2 days of symptoms reduced SAR from 10.6% to 4.5% (P= 0.003). The SAR in child contacts was 33.3% (10/30) when the index case-patient was a woman but only 2.9% (1/34) when it was a man. The authors conclude, "Prompt [antiviral] administration (either as treatment or prophylaxis) reduces symptomatic SARs."May 25 Emerg Infect Disstudy

Past flu season more deadly for UKIn its review of the 2010-11 flu season, the UK's Health Protection Agency (HPA) said today that the number of deaths exceeded the pandemic level seen the previous year and were highest in young and middle-aged adults. The HPA said it received 602 flu death reports during the last season, compared with 474 during the pandemic months. The 2009 H1N1 virus dominated the UK's 2010-11 season, and other studies have found older people—the group typically hit hardest by seasonal flu—appear to have some immunity to the virus. For all age-groups, 70% of patients with flu who died had risk factors for complications. Of those younger than 65 who were in high-risk groups and were recommended to receive the vaccine, only 50% were vaccinated, which was down from the year before, the HPA said. Though the vaccine was recommended for the first time for all pregnant women, only 37% received it.May 25 HPA press release

Imports helped swine flu in Hong Kong pigs to diversifyImporting pigs from Europe and North America over the past 30 years appears to have increased the genetic diversity of swine influenza in Hong Kong pigs through gene reassortment, according to a study today in Nature. Using 650 isolates and 800 serum samples collected over 12 years and supplemented with data going back 34 years, an international team studied the epidemiology, genetics, and antigenic properties of swine flu viruses in Hong Kong. From August 1998 to December 2002, the isolates were mostly classical swine (CS) H1N1 viruses. Eurasian avian-like (EA) H1N1 viruses—for which humans have no antibodies—were detected from 2001 on, and a triple-reassortant (TRIG) H1N2 beginning in 2002. From 2002 through 2005, CS, EA, TRIG, and H3N2 co-circulated and fluctuated in prevalence. EA viruses began to dominate in 2006 as H3N2 disappeared, while CS and TRIG flu continued to be isolated sporadically. Pandemic 2009 H1N1 joined the mix in 2009. The authors write, "Intercontinental virus movement has led to reassortment and lineage replacement, creating an antigenically and genetically diverse virus population." Vijaykrishna Dhanasekaran, PhD, of Duke University, a study co-author, said the increased genetic diversity "means that the repertoire of viruses that humans are in contact with every day has increased, and this may lead to a higher likelihood of swine-to-human transmission, although the risk remains unquantified."May 25 NaturestudyMay 25 Duke press release

Study: Combining seasonal and H5N1 flu shots is feasibleA study in the Journal of Infectious Diseases(JID) suggests that a seasonal influenza vaccine and an adjuvanted H5N1 vaccine can be combined or given at the same time without impairing their immunogenicity or safety. The researchers say that combining the two vaccines would be a useful way to prime the population for a potential H5N1 pandemic. The H5N1 vaccine used in the study contained the MF59 adjuvant, made by Novartis, which sponsored the trial. The researchers recruited 401 young, healthy adults and randomly assigned them to receive the two vaccines either separately and concomitantly, in a single injection mixed just before administration, or 21 days apart. Some of the volunteers also received a second H5N1 dose on day 22. In all three presentations, the seasonal vaccine met European immunogenicity criteria for licensing. The H5N1 vaccine induced seroprotection rates of 28% to 40% after one dose and 67% to 80% after two doses, the latter being sufficient to meet the licensing criteria. Solicited adverse events were mild to moderate, and no serious adverse events were reported. The report says the findings support "the feasibility of incorporating prepandemic MF59-adjuvanted A/H5N1 vaccines into seasonal influenza vaccination programs and the development of tetravalent influenza vaccines, including pandemic strains."June JID report

Sports fans may risk vuvuzela spewResearchers found that blowing vuvuzelas—those plastic horns used by zealous sports fans, notably at the World Cup in South Africa—releases almost 200 times as many respiratory particles into the air as does simply cheering on the home team. British researchers asked eight healthy volunteers to blow a vuvuzela and shout, and then collected particles from the exhaled air. They found that horn blowing produced 658,000 particles per liter of air, compared with 3,700 particles per liter for shouting. The particles were almost exclusively (97%) from 0.5 to 5 microns in diameter. The authors write that "vuvuzelas have the capacity to propel extremely large numbers of aerosols into the atmosphere of a size able to penetrate the lower lung," noting that aerosol spread is likely with diseases such as influenza, the common cold, chickenpox, and pneumococcal disease.May 23 PLoS Onestudy